1. Field of the Invention
The present invention relates to an orthodontic appliance, particularly relates to an orthodontic bracket made of plastic, and an archwire engaged to the bracket.
2. Description of the Related Art
So far, as the orthodontic bracket as an essential part of an orthodontic appliance, various materials such as metal, ceramics, plastics and the like have been employed. The orthodontic bracket has respective merits and demerits depending upon the material (raw material) of which it is made.
For example, the metal orthodontic bracket has a mechanical strength required in the orthodontic treatment, but has a demerit that the metal color will attract attention when a mouth is opened, giving an aesthetically undesirable impression.
The ceramic orthodontic bracket is aesthetically more excellent than the metal one, but has a demerit, for example, that the ceramics is materially harder than tooth enamel. This will often abrade occluded teeth and cause the archwire to be abraded as well. Further, since the ceramic orthodontic bracket is materially fragile, the bracket will be often cracked when it is applied with torque by an angular wire. Further, there may be a trouble that the tie wings supporting the ligature will be broken when the archwire is tied to the bracket.
Further, the ceramic orthodontic bracket has a high friction resistance compared with the metal one and will detract the slide property of archwire. Namely, the ceramic bracket tied onto the archwire will not smoothly slide along the archwire. This will prevent the effective movement of tooth and cause the orthodontic treatment to take more time.
The plastic orthodontic bracket is superior in moldability (processability), but has a demerit, for example, that aesthetic property will be lost due to the progress of discoloration and deterioration by chemical components and pigments contained in foods. Further, the plastic orthodontic bracket is inferior in mechanical strength compared with the metal one.
Especially the recent orthodontic bracket has been required to have a special aesthetic property in addition to the fundamental function required in orthodontics.
Therefore, the ceramic orthodontic bracket and plastic orthodontic bracket have come to be generally employed.
As to the ceramic orthodontic bracket and plastic one, the slot portion is, for example, contrived as is replaced by metal or other material to reinforce the slot portion and simultaneously decrease its friction resistance, and further the metal is provided as a core material (reinforcing member) inside of the bracket (U.S. Pat. No. 5,595,484).
Recently, resins of low water absorption have been developed, which will not be discolored, for example, by coffee having a relatively strong pigment.
Under these circumstances, demand for the plastic orthodontic bracket has been increased. The plastic orthodontic bracket is generally made of polycarbonate(PC) because the polycarbonate is superior in transparency, chemical stability, impact resistance, dimensional precision when molding in addition to non-poisonous property, thereby to heighten the adaptation for the orthodontic bracket.
Thus, the plastic orthodontic bracket is superior in aesthetic effect and has come to be generally employed. However, the plastic orthodontic bracket has some problems remaining unsolved.
First of all, the problem is the solvent crack. Generally, the orthodontic bracket is directly adhered to a tooth by a dental adhesive. Therefore, in case the plastic bracket has an inner stress therein at the time of being molded (inner stress due to distortion generated when molding), the plastic bracket will often react to an organic solvent contained in the adhesive to produce the solvent crack at the bracket base and wings. As a result, the plastic bracket reduces the strength thereof to about {fraction (1/10)} of the standard strength rendering the plastic bracket to be useless.
In this respect, there has been an inconvenience that a specific adhesive, which will produce no possible problem, has to be selected in consideration of the compatibility between the plastic material for the orthodontic bracket and the solvent contained in the adhesive.
A second problem is lowered strength and aesthetic property due to the hydrolysis of synthetic resin.
Namely, it may be considered that the hydrolysis of polycarbonate is encouraged by the cut of ester coupling because carbonyl group is easily coupled to water molecule. Thus, the strength is reduced to a half of the original strength in about one year in the mouth of human body temperature. Further, the polycarbonate will easily be hydrolyzed if it has a high percentage of water contained before being molded. As results, it comes to invite the degradation of quality including bubbles created in the molded member, lack of surface luster, uneven fluidity, and lack of tensile strength and durability. Further, it is generally known that the plastics susceptible to hydrolysis will easily propagate microbes which produce the hydrolysis enzyme (enzyme for catalyzing hydrolysis) to accelerate the hydrolysis.
A third problem is adhesion strength.
Namely, it is preferable that the plastic orthodontic bracket is made of a resin of low water absorption which will produce no hydrolysis for a long period of time to maintain a desirable aesthetic property. However, the synthetic resin of low water absorption lacks the compatibility to the adhesive for obtaining sufficient adhesion strength to fix the resin to the tooth.
The plastic bracket having a reinforcing structure will be further specifically explained.
For example, the following plastic brackets having the reinforcing structure have been known. Namely, as disclosed in U.S. Pat. No. 4,299,569 and JP-A-9-98988, a metallic slot liner is provided in a mediodistal direction. As disclosed in U.S. Pat. Nos. 5,595,484, 5,813,852 and 5,597,302, a metal member having U-shaped cross section is insert-molded in the direction perpendicular to the slot.
In the metal slot liner structure and the metal insert structure, during the injection molding process, the liner and the insert member is disposed in an injection molding die prior to molding. Then, the resin encloses the liner and the insert member by the injection molding to form the plastic bracket. In this case, the resin for use is transparent or translucent and has high aesthetic property, such as polycarbonate, acryle, polyuretane and polyacetal, which are adhesive and water-resistant. However, in the molding process, during solidification of the resin by cooling, large residual stress occurs on the inside of the resin due to difference of expansion coefficients between the metallic liner/the insert member and the matrix resin.
Thus, in the structure in which the metallic liner and the insert member are integrally molded, comparatively large residual stress exists therein. Consequently, as described above, the plastic bracket senses to react with the adhesive solvent so as to cause the solvent crack when the bracket adheres to the tooth surface. Further, due to the existent residual stress, some kinds of resins accelerate the hydrolysis as described above. Thus, the tie wing or the like is broken before the generally required orthodontic treatment period (18 to 24 months).
Further, it has been generally performed that silane-coupling-treated inorganic filler, which is glass filler, is mixed to the matrix resin in an amount of 10 wt % to 50 wt %, to thereby enhance the mechanical strength. For example, as disclosed in U.S. Pat. Nos. 4,717,341 and 5,254,002, in the orthodontic appliance, the physical property and the durability of the bracket and the archwire are enhanced within such range as not to lower aesthetic property.
Glass filler is dispersed into the plastic bracket so as to enhance the cracking resistance property and the rigidity. Simultaneously, micro inner stress occurs. That is, a matrix resin having high inner stress exists around glass filler because of the difference of the thermal expansion coefficients between glass filler and the matrix resin when the resin is cooled and solidified at the time of injection molding. This micro inner stress (residual stress) is not actualized when the solvent of the orthodontic adhesive only temporally attached to the resin.
However, when the plastic bracket containing glass filler in the range of 10 wt % to 30 wt % was immersed in a test solution containing carbon tetrachloride and butanol in the ratio of 50:50 for one minute, the bracket was wholly whitened. This is because micro cracks are generated at portions having high inner stress around glass filler. Incidentally, the plastic bracket is not directly broken by these micro cracks. However, there is a problem that the durability is lowered by hydrolysis.
A metallic wire is mainly used as an orthodontic archwire. In order to enhance aesthetic property, a metallic wire as a core material is coated with fluorocarbon resin, whose color is close to white or tooth color. However, in this case, since the archwire is opaque, there is room for improvement regarding aesthetics.
In addition, there is a translucent archwire in which an optical fiber is used as a core material. However, since the orthodontic force is weak, its usage is restricted and it can not be suitable for practical use.
The objective of the present invention is to provide an orthodontic appliance capable of preventing the solvent crack in a bracket and maintaining a sufficient strength for a long period of time in the mouth. In the case of a bracket, the objective of the present invention is to provide the orthodontic appliance capable of obtaining sufficient adhesion strength.
In the case of an archwire, the objective of the present invention is to provide the orthodontic appliance that exhibits excellent capacities, e.g., optimal orthodontic force, aesthetic property and the like.
In this invention, orthodontic appliances that fit into the mouth as orthodontic means, at least an orthodontic bracket and/or an archwire comprise a component constructed by dispersing a thermoplastic elastomer in a matrix resin.
The above orthodontic appliance of the present invention is characterized in that:
the matrix resin is a polycarbonate resin and the thermoplastic elastomer is a styrene elastomer;
the content of the styrene elastomer is 0.5 wt % to 10 wt %;
the content of the styrene elastomer is 0.5 wt % to 2.0 wt %;
a particle size of the styrene elastomer is 0.1 xcexcm to 10 xcexcm;
a reinforcing member is provided at a slot of the bracket that is exposed to an inner wall surface of the slot so as to reinforce said inner wall surface;
the reinforcing member is extended and embedded into the tie wings which are formed as being extended towards the gingival side and occlusal side of the slot;
the reinforcing member has a hook core member provided to reinforce a hook of the bracket; and
the matrix resin contains inorganic filler.
In the orthodontic appliance of the present invention, at least an orthodontic bracket and/or an archwire comprise an component constructed by dispersing a thermoplastic elastomer in a matrix resin. Accordingly, many voids formed by the elastomer can release strain which is a factor of stress concentration. Therefore, the orthodontic appliance can maintain the strength for use in the mouth for a long period of time.
In the orthodontic appliance of the present invention, the matrix resin is a polycarbonate resin and its thermoplastic elastomer is a styrene elastomer. Accordingly, myriad voids formed by the elastomer can further surely release strain which is a factor of stress concentration. Therefore, the orthodontic appliance can maintain the strength of use in the mouth for a long period of time.
In the orthodontic appliance of the present invention, the content of said styrene elastomer is 0.5 wt % to 10 wt %, and preferably, the content of said styrene elastomer is 0.5 wt % to 2.0 wt %. Accordingly, many voids formed by the elastomer can further surely release strain which is a factor of stress concentration. Therefore, the orthodontic appliance can favorably maintain the strength for in the mouth for a long period of time. Furthermore, if a particle size of said styrene elastomer is 0.1 xcexcm to 10 xcexcm, it is possible to obtain further stable strength.
In the orthodontic appliance of the present invention, reinforcing member is provided at a slot of the bracket. Said reinforcing member is exposed to an inner wall surface of the slot so as to reinforce said inner wall surface. Accordingly, the strength of the slot is enhanced and the orthodontic force can be surely applied to the slot for a long period of time.
In the orthodontic appliance of the present invention, the reinforcing member is extended and embedded into the tie wings which are formed as being extended towards the gingival side and occlusal side of the slot. Accordingly, it is possible to enhance the strength of the tie wings. Further, even if the tie wing is broken, it is possible to temporarily maintain ligature by the reinforcing member only.
In the orthodontic appliance of the present invention, the reinforcing member has a hook core member provided to reinforce a hook of the bracket. Namely, the reinforcing member is extended and embedded into the hook. Accordingly, the strength of the hook is enhanced and its application of the orthodontic force can be assured.
In the orthodontic appliance of the present invention, the matrix resin contains an inorganic filler. It is possible to not only enhance the resin strength but also adjust the transparency of the resin. Further, since both thermoplastic elastomer and glass filler exist in the synthetic resin, the solvent resistance of the orthodontic appliance is enhanced. Further, since the inner stress generated by glass filler is absorbed, it is possible to prevent micro cracks and suppress hydrolysis in the mouth.
An orthodontic bracket of the present invention having one end side surface fixed to a tooth and having the opposite end side formed with a slot which is designed to be engaged by an arch wire; comprises a composite resin having a first synthetic resin for providing a strength of the orthodontic bracket in the mouth and a second synthetic resin for providing an adhesion property thereof.
The above orthodontic bracket is characterized by:
the first synthetic resin that includes polyethylene-terephtalete and the second synthetic resin that includes polycarbonate which ranges 30 to 80 wt %;
said orthodontic bracket further comprises a bonding base area for providing a surface to be adhered to a tooth and a bracket member area which is continuous to the bonding base area and is formed with the slot and tie wings; wherein polycarbonate contained in the bonding base area is in the range of 60 to 100 wt %, and polyethylene-terephtalete contained in the bracket member area is 60 to 100 wt %; and
the synthetic resin contains inorganic filler therein.
The orthodontic bracket of the invention has one side surface to be fixed to a tooth and has the opposite side having a slot formed thereat so as to be engaged by an arch wire, comprises a composite resin including a first synthetic resin for maintaining a strength of the orthodontic bracket to be used in the mouth and a second synthetic resin for providing an adhesion property of the orthodontic bracket, the first synthetic resin being effective to maintain the orthodontic bracket to be used for a long period of time in the mouth, and the second synthetic resin being effective to secure an adhesion strength between the orthodontic bracket and the tooth.
According to the orthodontic bracket of the invention, polyethylene-terephthalete is used as the first synthetic resin and polycarbonate is used as the second synthetic resin, and polycarbonate ranges 30 to 80 wt % particularly for suitably maintaining the adhesion strength and the strength within mouth, and the rate of polyethylene-terephthalete (20 to 70 wt %) is used to remarkably reduce the residual stress at the time of molding, thereby to avoid the risk of the solvent crack.
The orthodontic bracket of the invention comprises a bonding base area providing thereat a surface to be adhered to a tooth and a bracket member area providing the slot and tie wings thereat which are continuous to the bonding area, and the bonding base area is formed with polycarbonate of 60 to 100 wt %, thereby to enable the polycarbonate of high adhesion strength to be used as a material for a portion to be adhered to remarkably increase the adhesion strength, and the bracket member area being is with polyethylene-terephthalete 60 to 100 wt %, thereby to enable the polyethylene-terephthalete to be used as a material for the bracket which is to be exposed in the mouth to remarkably increase the strength in the mouth.
An orthodontic bracket of the present invention having one end side surface fixed to a tooth and having the opposite end side formed with a slot which is designed to be engaged by an arch wire, comprises a reinforcing member provided in a bracket made of a synthetic resin so that a part of the reinforcing member or a base member fixed to the reinforcing member is exposed at a base surface which is positioned against the tooth.
Said orthodontic bracket is characterized by:
a rear surface of a bottom of the reinforce member or a rear surface of the base member is slightly recessed from the base surface;
the reinforce member is extended and embedded into the tie wings which are formed as being extended towards the gingival and occlusal sides of the slot;
the rear surface of the bottom of the reinforce member or the base member has a surface facing the tooth, the surface being rugged or meshy;
the synthetic resin is polyether-sulfone;
the synthetic resin is a composite resin; and
the synthetic resin contains inorganic filler therein.
According to the invention, the orthodontic bracket has a reinforcing member provided in the bracket made of synthetic resin, a part of the reinforcing member or a base member fixed to the reinforcing member is exposed at a base surface which is to be positioned against a tooth. Accordingly, the reinforcing member can be directly adhered to the tooth.
According to the orthodontic bracket of the invention, the reinforcing member has a bottom having a rear surface or a base member having a rear surface, and the rear surface of the reinforcing member or the rear surface of the base member is slightly recessed from the base surface. Therefore, the recessed portion may receive the adhesive therein.
According to the orthodontic bracket of the invention, the reinforcing member is extended and embedded into the tie wings. Accordingly, the strength of tie wings may be increased, and further the reinforcing member may temporarily maintain ligature in case the tie wings are broken.
According to the orthodontic bracket of the invention, the bottom of the reinforcing member or the base member has a surface which is to be against the tooth, and the surface is rugged or meshy. Therefore, the contact area of the surface may be increased or may produce an anchor effect to the adhesive.
According to the orthodontic bracket of the invention, the synthetic resin is polyether-sulfone which is harmless to human body and superior in durability.
According to the orthodontic bracket of the invention, the synthetic resin has inorganic filler, more particularly, glass filler contained therein. Therefore, it is possible to increase the strength of the synthetic resin, and further to adjust the transparency of the resin.